Why does the car need warming up every time it's restarted?

<div class='quotetop'>QUOTE(PriusRos @ Jul 30 2006, 10:33 AM) [snapback]294603[/snapback]</div>

I'm sure there are others who can give a more technical answer, but you should bear in mind that when the engine is warming up, it is the ICE we're talking about here, not the battery, the electric motor, or anything like that. The car doesn't know that you're going to be driving at a low speed as opposed to immediately hitting the freeway.

The ICE also runs at first after you turn on the car in order to make sure it is working. If you got up to speed using your electric motor, only to discover in motion that the ICE wasn't functioning when you need it, that would be... well, bad. This way, you and the car will know if everything is working properly within seconds of starting the car.

 

The ICE turns on about 7 seconds after each start to get the catalytic converter warmed up so the emissions are better (I guess a cold cat doesn't perform as well). Unless you have the EV switch/button, the car is programmed to do it on every start.

The speed limit on my street is 35 mph, but I have found that if it get the car up to 42 mph and then back off to 35 or less, the car will go into battery mode more quickly/easily than if I don't pass the magic "41". I don't know the technical reason for it, but I think getting the car into the "must use ICE mode" tells it that it's OK to turn off if you're below that speed. There's another way I could go that's posted at 25 mph, and my 5-minute mileage is worse if I take that way.

FWIW, YMMV

 

Maybe this will help you understand more? The Five Stages of Prius Operation

 

<div class='quotetop'>QUOTE(PriusRos @ Jul 30 2006, 11:33 AM) [snapback]294603[/snapback]</div>

I'd like to check that out, what is the name of the forum???

 

google EPA test cycles and see why most people never get the EPA rating. It's totally unrealistic the procedure that they use to get their estimate. If you drive like that you will get their milage OR better if you really try.

 

<div class='quotetop'>QUOTE(Frank Hudon @ Jul 30 2006, 09:55 PM) [snapback]294852[/snapback]</div>

Someone had a detailed description of the EPA procedures here as well. And your response is dead on: the EPA "city" driving is nothing like what I consider city driving. I live in Downtown Dallas and every morning my drive to the freeway is about 1.5 miles of stop and go driving. I hit a red light about every quarter mile at best, and every eight of a mile at worst. My city mileage is horrible, but it's nothing like what the EPA considers city driving.

I would probably call the EPA "city" estimate "small town" instead, as when I used to live in a small town in Ohio I could go between 20 and 35 for a mile or two at a time and I would probably get great gas mileage there.

And by the way, I also get great gas mileage driving on the freeways around 70mph. Twenty minutes out of my thirty minute commute are always at 50+ MPG, it's just too bad that the five before and after that are all MPG-killers.

 

Same here. I have always gotten better mileage on the highway. I get the best mileage on country roads at about 35 to 45 MPH with few stops. Then mileage is in the 60s!

 

You may want a way to monitor the engine temp and coolant temp. If they have dropped below 160 F the engine needs to heat up. I know of no way to monitor the converter temperature. I suspect it is on the CAN -BUS because it is important to full Hybrid operation. Look at the 4 stages. The engine temp need to be up but you need the brief rest until the ICE goes off. Then you are in Stage 4.

 

See http://www.fueleconomy.gov/feg/how_tested.shtml and http://www.fueleconomy.gov/feg/fe_test_schedules.shtml for a summary of the details.

The first page also mentions "A hose is connected to the tailpipe to collect the engine exhaust.

The amount of carbon in the exhaust is measured to calculate the amount of fuel used during the test.

This is more accurate than using a fuel gauge." I've heard they measure the amount of unburned hydrocarbons.

Also, since these procedures were devised way before hybrids, maybe there's nothing to dictate what the SOC of the battery is. For all we know, Toyota could be fully charging the battery before starting the test (and still be within the rules).

 

<div class='quotetop'>QUOTE(Adam Sills @ Jul 30 2006, 11:49 PM) [snapback]294883[/snapback]</div>

Yeah, as someone who lives in small-town northwest Ohio (where it is COMPLETELY FLAT geographically) I can tll you that enjoy being able to go all the way from I-75 to my home in downtown B.G. almost completely on the battery... and I dont usually experience that many stops... mostly as no matter what direction I go from downtown B.G there are no more than 7 stop lights to the countryside... so small town living has its advantages... And I just drove from Port Columbus Int'l airport to Bowling Green from I-670 to 2-70 to US 23 to I-75 and then to Bowling Green driving at 70 MPH and averaged 49.4 MPG this evening.... so yay to flat places...! I can drive down to Ft. Campbell Kentucky getting 53 MPG and 48+ on the return trip also... so the prius can handle hills and mountains too... I never stop falling in love with this car!

 

<div class='quotetop'>QUOTE(PriusRos @ Jul 30 2006, 07:34 PM) [snapback]294842[/snapback]</div>

I suspect here you've gotten to the heart of the matter---or at least the likeliest big difference: the EPA tests are not conducted as short errands.

 

dont know if anyone has addressed this yet, but the OP's assertion that his mileage is no better on the first 5 minutes whether his Prius sits overnight or is being restarted in the midst of several runs on a warm sunny day is something i rarely see.

even with temps as low as 70º (average HIGH summer temps here is 75º) my first bar after restart is nearly always higher, usually in the 40-50 mpg range as opposed to the 20-30 mpg range. i have actually tracked this frequently along with how long it takes my Prius to warm up to what i would consider the "minimum efficient operating temperature" of 155º and on warm summer days if allowed to get to 185º, it can take as much as an hour before i get the "first thing in the morning" mileage.

OAT is a HUGE factor, but i do know that the warmer the temps get, the better the mileage. i am on the 3rd 60 mpg tank but only because we have had temps running 15-25º above normal. currently at 65.6 mpg @154 miles. but the temps are now back to normal and my average will drop probably to the high 50's.